Nafion/Protic Ionic Liquid Blends: Nanoscale Organization and Transport Properties

Abstract

In this work, the possibility of using the protic ionic liquids N-ethylimidazolium trifluoromethylsulfonate, [EIm][TfO], and N-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [EIm][TFSI], as charge carriers in appropriately modified Nafion membranes has been investigated. The superior thermal stability of ionic liquids, as compared to that of water-based electrolytes, hypothetically offers a wider temperature range of fuel cell operation as well as an increased electrochemical performance even at low-humidity conditions. The nano-and microstructure of Nafion membranes swollen with these protic ionic liquids has been studied in detail, with focus on the correlation with the observed ionic conductivity. Although the presence of the ionic liquid within the hydrophilic domains of Nafion suppresses the thermomechanical properties of the polymer, satisfactory conductivities are achieved between 90 and 150 °C, namely, in the range 0.2−1.2 × 10 −3 S/cm.

Self-Standing, Robust Membranes Made of Cellulose Nanocrystals (CNCs) and a Protic Ionic Liquid: Toward Sustainable Electrolytes for Fuel Cells

“…In addition, the membrane containing [HC 6 Im]­[TfO], which is also the composite with the higher ionic liquid content, displays a higher ionic conductivity. Most importantly, the values found for these composites are comparable to those measured for other more established polymer/protic ionic liquid electrolyte concepts. ,, However, the CNC-based electrolytes presented here provide a higher thermal stability than those based on Nafion or other perfluorinated polymers that, apart from dehydration, also suffer from mechanical weakening at temperatures above their T g (e.g., the T g of Nafion is ∼90 °C). From an Arrhenius plot of the measured conductivity values (Figure b), we could estimate the activation energy E a , which decreases from 44 kJ/mol (0.45 eV) for the precursor CNC/Im to only 27 kJ/mol (0.28 eV) for the CNC/Im/[HC 6 Im]­[TfO]­(80) composite.…”

“…In this work, we exclusively consider films based on CNCs. The choice of imidazolium-based protic ionic liquids relies on our previous studies and includes the immiscibility with water as an important aspect. In fact, although we aim for the anhydrous operation of the polymer electrolyte, water is the product of the oxygen reduction reaction at the cathode of a PEMFC, which brings along the risk of washing out the water-miscible components.…”

Influence of Counteranion on the Properties of Polymerized Ionic Liquids/Ionic Liquids Proton-Exchange Membranes

“…The two composites are able to maintain a high modulus from room temperature to 120 °C, suggesting a good mechanical stability for high-temperature application. However, the highest-temperature relaxation (α) observed in Figure is associated with the breakage of interactions between the ionic groups, which causes the mechanical strength loss . This demonstrates an obvious plasticizing effect of protic ILs on the polymer matrix because of the much lower T α values than that of neat [PDADMA]­[TFSI] at 120 °C .…”

“…However, the highest- temperature relaxation (α) observed in Figure 4 is associated with the breakage of interactions between the ionic groups, which causes the mechanical strength loss. 27 This demonstrates an obvious plasticizing effect of protic ILs on the polymer matrix because of the much lower T α values than that of neat [PDADMA][TFSI] at 120 °C. 28 In contrast, the OTfonly and H 2 PO 4 -only composites are too fragile to be measured, suggesting the poor plasticizing effect of the OTf and H 2 PO 4 anion.…”

Stereolithography Provides Access to 3D Printed Ionogels with High Ionic Conductivity

“…This results from the O–H stretching in the water contained in the ionic liquids. Finally, broad bands around 1700 cm –1 can be assigned to H 3 O + vibrations, where the H 3 O + forms in a proton transfer reaction between IL and water. , Bands between 1600 and 1200 cm –1 are assigned to C–H deformation vibrations, N–CH 3 – and N–CH 2 stretching vibrations of the ring systems, and C–C stretching vibrations; bands between 680 and 560 cm –1 result from the corresponding deformation vibrations. Of particular interest to this study are the three sulfonate bands in the range of 680–580 cm –1 (bending vibrations), 1030–1000 cm –1 (symmetric stretching vibrations), and 1170–1120 cm –1 (asymmetric stretching vibrations), , proving the presence of sulfonate groups in the ILs.…”